After first meeting at a summer camp as teenagers, Emma (Natalie Portman) and Adam (Ashton Kutcher) run into each other a few times as young adults but never keep in touch. Emma becomes a hospital resident in Los Angeles, Adam a production assistant for a musical television show. Adam's father Scott (Kevin Kline), the well-known star of a former hit television comedy series, has begun a romance with Adam's ex-girlfriend, Vanessa (Ophelia Lovibond). Adam finds out, gets drunk and calls the women in his phone seeking a hookup. The next morning, he wakes on a sofa wearing nothing but a small towel. It turns out that he texted Emma and then came to the apartment she shares with some other residents — Patrice (Greta Gerwig), Shira (Mindy Kaling), and Guy (Guy Branum). Once there, he took off all his clothes and then passed out. Emma leads Adam to her bedroom to retrieve his missing pants and they end up having sex.

The two have sex again at Adam’s house and before she leaves Adam agrees to her proposal for a casual relationship (as she puts it, using each other for sex and nothing else). Adam warns Emma about falling in love with him, but she dismisses the idea and sets ground rules to keep what they’re doing from becoming too serious. At first things go well, but Adam becomes jealous when Sam (Ben Lawson) — another resident — seeks her attention. Adam brings Emma a gift (a mix CD) and she rebuffs him, saying they should stop for a while and hook up with other people. But after being apart for two weeks Emma returns to Adam and they continue being sex friends only.

Adam's birthday comes along a few months later. He goes out for dinner with Scott and Vanessa, who announce their plan to have a baby together. Emma berates the other couple while defending Adam. He persuades her to go out together on Valentine's Day. Things fall apart when she becomes too uncomfortable during the date. An angry Emma advises Adam that he should find someone else who won’t hurt him. Adam tells Emma that he loves her — something she's not at all receptive to hearing — they have a fight, ending their arrangement.

Six weeks later, a script Adam wrote is being filmed. He gets a regular writing job on the show with the help of Lucy (Lake Bell), the show's assistant director (Jennifer Irwin), who is clearly attracted to Adam. Meanwhile, Emma is depressed over not being with Adam. The situation is compounded and complicated by her younger sister Katie's (Olivia Thirlby) wedding the next day and her widowed mother (Talia Balsam) arriving for the event with a male companion (Brian Dierker) of her own. Emma feels she is being strong for her mom by not letting herself get too close to anyone so she won't become upset by seeing Emma get hurt if a relationship ends poorly. Emma's mom tells her to stop.

When Emma confesses that she can't stop thinking about Adam, Katie insists that she call him to put things right. A nervous Emma phones Adam and tells she misses him. His responds that they were never really together. Realizing that she needs to speak with him in person, Emma leaves Santa Barbara where the wedding is taking place and drives to Adam's house. Her plans are ruined – and she has to hide to avoid being seen — when he arrives home with Lucy. Emma assumes Adam has a new girlfriend and tearfully drives away. Vanessa calls Adam before he and Lucy can have sex — Scott has overdosed on a cough syrup-based drink called "Purple drank". Meeting Adam outside the hospital, Vanessa says that she is ending her relationship with Scott and leaves for a party. Adam goes in to visit Scott who surprisingly gives him some tender advice about falling in love.

Shira tells Emma about Adam's dad being admitted to the hospital. As Adam leaves the building he calls Emma and tells her that she must be present if she is going to say that she misses him. Emma gets out of her car as the call ends and Adam is stunned to suddenly find her there. She tells Adam that she is sorry she hurt him and confesses that she really loves and cares about him and they reconcile. After eating breakfast together the next morning — something that never happened before — they arrive in Santa Barbara just before Katie's wedding is starting. As they enter a room and pause Emma asks Adam what will happen next, and with a smile on his lips he silently intertwines her hand with his — for the first time they are holding hands together as a couple.

The end credits show an epilogue in which; Scott and Lucy are in a relationship and in a restaurant waiting for Adam to arrive to tell him. Adam’s roommate (Jake Johnson) and Patrice are in a relationship and are shown meeting his two dads. Vanessa had told Adam that old people scare her and she is ridden with anxiety when she is trapped in an elevator full of senior citizens. Adam and Emma are seen kissing in the park. Sam and Shira are in a relationship, but he wants his freedom and isn't pleased when she reveals that she’s already been seeing other men. Katie is having a baby and Emma is the delivering doctor. Guy lures a nervous-looking Sam into a hospital room. At last, Adam and Emma are shown peacefully sleeping together.

No Strings Attached is directed by Ivan Reitman based on a screenplay by Elizabeth Meriwether titled Friends With Benefits.[citation needed] The title was changed to avoid confusion with a different film with a similar premise that opened on July 22, 2011. The Paramount Pictures film was first announced in March 2010 as an untitled project. Actors Ashton Kutcher and Natalie Portman were cast in the lead roles, and Paramount anticipated a release date of January 7, 2011.[3] Reitman said of casual sex, "I noticed from my own kids that with this generation in particular, young people find it easier to have a sexual relationship than an emotional one. That is how the sexes deal with each other today."[4] Principal photography began in May 2010.[5] By November 2010, the film was titled No Strings Attached with a new release date of January 21, 2011.[4]

Though the timing was coincidental, Portman welcomed the chance to portray a dissimilar character to her role in Black Swan.[6]

No Strings Attached had its world premiere on January 11, 2011, at the Fox Village Theater in Los Angeles, California.[7] The film was released in 3,018 theaters in the United States and Canada on January 21, 2011.[2] Its target demographic was women between 17 and 24 years old, and its primary competition was The Dilemma.[citation needed] Interest tracking reflected the target demographic's gaining interest in the film leading up to its release, and tracking also revealed "good early awareness" from Hispanic audiences.[citation needed] The studio predicted for the film to gross in the "mid-to-high teens" millions in its opening weekend,[8] similar to past romantic comedies rated "R" (restricted to 17 years old and up) by the Motion Picture Association of America. With No Strings Attached as the only wide opener in the United States and Canada, it was uncertain if it would rank first at the box office above The Green Hornet, which opened the previous weekend in first place with $33.5 million.[1]

Ultimately, No Strings Attached beat The Green Hornet with an opening weekend gross of $20.3 million. 70% of the audience were women.[9] According to CinemaScore, audiences under the age of 25 gave the film an "A-" grade while audiences over the age of 25 gave it a "B" grade. Future grosses were expected to be dependent on the younger demographic.[10]

The film has grossed $70.7 million in the United States and Canada and $77.1 million in other territories for a worldwide total of $147.7 million.[2]

No Strings Attached received mixed reviews. Review aggregator Rotten Tomatoes gives the film a rating of 49%, based on 164 reviews, with an average rating of 5.2 out of 10. The site's consensus reads: "It benefits from the presence of Natalie Portman and director Ivan Reitman's steady hand, but No Strings Attached doesn't have the courage or conviction to follow through on its ribald premise."[12] On Metacritic, the film received an score of 50 out of 100, based on 36 reviews, indicating "mixed or average reviews".[13]

Critic David Edelstein described No Strings Attached as a film with "a supposedly feminist veneer...(that) never makes the case for Emma's point of view. It's almost a feminist backlash movie, and it didn't have to be. There are plenty of reasons for brilliant young women, especially with the stress of a medical career, to approach time- and emotion-consuming relationships warily." He expressed disappointment on overuse of stock characters, as well as Reitman's "heavy-handed" direction and a story that is ultimately "corny and contrived and conservative."[14]A. O. Scott called the film "not entirely terrible...high praise indeed, given that this is a film aspiring to match the achievement of 27 Dresses, When in Rome and Leap Year"; according to Scott, the film is "Love & Other Drugs without the disease", a film whose pleasures "are to be found in the brisk, easy humor of some of Ms. Meriwether's dialogue and in the talented people scattered around Ms. Portman and Mr. Kutcher like fresh herbs strewn on a serving of overcooked fish."[15] Scott considered "the film's great squandered opportunity—and also the source of some of its best comic moments—is that Ms. Gerwig and Mindy Kaling in effect share the role of Emma’s zany sidekick. How can this be? Why are these two entirely original and of-the-moment performers marginal players in this agreeable, lackluster picture and not stars of the year’s greatest girl-bromance?... To imagine Ms. Kaling and Ms. Gerwig in a remake of Thelma and Louise or the Wedding Crashers is to experience an equal measure of frustration and hope. Why can’t we have a few movies like that and not quite so many like this?"[15]

British newspaper The Telegraph named No Strings Attached one of the ten worst films of 2011, saying "No Strings Attached is nominally a raunchy romantic comedy, but Natalie Portman betrays so little indication of enjoying herself you’d be forgiven for thinking we were watching deleted scenes from Black Swan."[16]